This invention relates generally to a method for determining the efficiency of a catalyst coating and more particularly to a method for determining the effectiveness of a catalyst based ozone depletion system.
The invention is particularly applicable to and will be described with specific reference to an on-board diagnostic system determining failure of an ozone depletion system applied to heat exchange surfaces in a vehicle and indicating such failure to the vehicle""s operator. However, the invention is believed to have broader application and could be employed to determine the conversion efficiency of a stationary system using a catalyst based ozone depletion system such as heat exchangers or HVAC systems in residential, commercial or industrial facilities. Still further, the invention is also believed to have application to certain catalyst formulations, other than those utilized in an ozone depletion system, but which have distinguishing performance characteristics similar to those of a catalyst based ozone depletion system.
The following United States patents are incorporated by reference herein and made a part hereof:
a) U.S. Pat. No. 5,051,671 issued Sep. 24, 1991 to Crider et al. entitled xe2x80x9cProximity Sensor and Controlxe2x80x9d;
b) U.S. Pat. No. 4,325,255 issued Apr. 20, 1982 to Howard et al. entitled xe2x80x9cUltrasonic Apparatus and Method for Measuring the Characteristics of Materialxe2x80x9d;
c) U.S. Pat. No. 5,556,663 issued Sep. 17, 1996 to Chang et al. entitled xe2x80x9cExcimer Fluorescence Method for Determining Cure of Coatingsxe2x80x9d;
d) U.S. Pat. No. 5,343,146 issued Aug. 30, 1994 to Kock et al. entitled xe2x80x9cCombination Coating Thickness Gauge Using a Magnetic Flux Density Sensor and an Eddy Current Search Coilxe2x80x9d;
e) U.S. Pat. No. 5,185,773 issued Feb. 9, 1993 to Blossfeld et al., entitled xe2x80x9cMethod and Apparatus for Nondestructive Selective Determination of a Metalxe2x80x9d; and,
f) U.S. Pat. No. 6,034,775 issued Mar. 7, 2000 to McFarland et al., entitled xe2x80x9cOptical Systems and Methods for Rapid Screening of Libraries of Different Materialsxe2x80x9d.
The above patents are cited so that the Detailed Description of this Invention need not recite in detail sensor apparatus and techniques known to those skilled in the art. None of the patents cited above or incorporated by reference herein form any part of the present invention.
i) Catalyst Based Ozone Depletion Systems
It is known that ground-level ozone, O3, is the main harmful ingredient in smog and at relatively small concentrations, ground level atmosphere is physically harmful. It is also known that ozone is produced by complex chemical reactions when its precursors such as VOC (volatile organic compounds) and NOx (nitrogen oxides) react in the presence of sunlight. The precursors mentioned are present in emissions produced from vehicles powered by internal combustion engines. The United States EPA has determined that cars and light trucks emit a substantial portion of precursors which produce ground level ozone.
The EPA, in implementing the provisions of the United States Clean Air Act, has identified 26 metropolitan areas within the United States which its modeling techniques show have or will exceed National Ambient Air Quality Standards for ozone in the near future. Accordingly, the EPA has promulgated increasingly tighter emission regulations directed to limiting emissions from vehicles which promote ozone formation.
It has been recognized for some time that a significant quantity of atmospheric air is used or drawn in by a vehicle while it is moving and that atmospheric air can be cleansed by the vehicle. For example, U.S. Pat. No. 3,738,088 to Colosimo passed a stream of atmospheric air drawn into a duct at the front of a vehicle through a filter and an electrostatic precipitator, powered electrically by the engine, which removed particulates from the atmospheric air before exhausting the cleansed air back into the atmosphere. Similar cleansing techniques have been widely used for purifying cabin air in a moving vehicle.
While there are various known ways or methods to remove or convert ozone to a benign chemical or compound, the assignee of the present invention has determined and formulated various catalyst coatings utilizing Manganese Dioxide, MnO2, which has been found effective to convert ozone to oxygen (O3xe2x86x923/2O2) at slightly elevated temperatures. Reference can be had to assignee""s U.S. Pat. No. 5,997,831, U.S. Ser. No. 09/151,784 filed Sep. 11, 1998 and Ser. No. 09/317,723 filed May 24, 1999 for examples of catalyst coatings which contain an ozone depleting substance, principally forms of MnO2, all incorporated by reference herein. Specifically, the assignee has determined that vehicles having radiators and/or air conditioning units operate at slightly elevated temperatures from ambient whereat the ozone depleting catalysts formulated by assignee are especially effective in converting ozone to oxygen while exhibiting characteristics allowing the catalyst to adhere to vibrating surfaces and function in the harsh environment that a motor vehicle is subjected to. The assignee of this invention has marketed its ozone depleting substances under its PremAir(copyright) brand name.
The environmental regulatory agencies have recognized the potential for vehicles to purify the atmosphere as well as being one of the causes of air pollution. To the extent that internal combustion engines produce emissions which cause the formation of ozone then, in principle, an offsetting xe2x80x9ccreditxe2x80x9d should and is allowed providing that a vehicle can be shown to reduce ground level ozone present in the atmosphere. In practice this requires an on-board diagnostic (OBD) system to determine the effectiveness of the vehicle to cleanse or convert ozone in atmospheric air to a clean form, i.e., O2.
Obviously, the most effective way to determine the functioning of an ozone depletion system is to measure the ozone concentration in the atmospheric air stream upstream and downstream of the ozone depletion system. The difference between the measurements provides an accurate xe2x80x9ccountxe2x80x9d of the quantity of ozone removed from the atmospheric air stream passing through the ozone depleting system. Another type of OBD system is widely used to determine the functioning of the typical TWC catalyst (three way catalyst) for removing HC (hydrocarbons) in that oxygen sensors, upstream and downstream of the TWC catalyst, sense upstream and downstream oxygen concentrations in the exhaust gas to estimate a storage capacity of the TWC catalyst which in turn is correlated to the efficiency at which the TWC catalyst converts certain noxious emissions.
A direct ozone sensing approach will not practically function today as an OBD system to measure the effectiveness of an ozone depletion system installed on a moving vehicle for several reasons. First, the ozone concentration that is being sensed is small and variable. For example, standard regulatory limits are 0.12 ppm over one hour with proposed regulations reducing the exposure to 0.08 ppm over an 8 hour period. Even in high smog concentration areas, such as Los Angeles, ground level ozone concentration may reach 0.20 ppm during summer, daytime hours and 0.01-0.02 ppm during nightime. The ozone sensor has to therefore have a sensitivity sufficient to detect and measure minute quantities of ozone present in a moving gas stream. Second, while current ozone detectors exist that can measure ozone concentration in the range of 100 ppb, the cost of current ozone sensors (priced in the thousands of dollars and not unusually, in the ten thousand dollar range) far exceeds that acceptable for an OBD application, even given the scales of economy achieved in the automotive market. Third the physical dimensions, response time and robustness of currently available ozone sensors is simply insufficient for an OBD system. For example many ozone sensors use a two step process of measuring light absorption through transmission measurements in an ozone free reference sample compared to an extracted ambient atmosphere sample to determine ozone concentration. Typically the detector requires a warm-up time and the sample volume is relatively large (although hand held) etc. Improvements are being made in such sensors. For example, U.S. Pat. No. 5,972,714 to Roland et al. discloses an ozone sensor measuring microcracks caused in an elastomeric material to determine the presence of ozone at sampling times in the range of 10-15 minutes. While a definite improvement, such sensor would not function as an OBD detector in the automotive environment.
ii) Sensors
The sensor art is a developed and refined field applied in any number of applications. In U.S. Pat. No. 4,325,255 ultrasonic impedance is measured to determine characteristics of a material including the density of the material, the level of material in a container, interface position between materials of different density, material hardness, particle and changes in chemical composition such as changes in physical/chemical characteristics i.e, density used to monitor the curing of resins, concrete and similar materials. In U.S. Pat. No. 5,051,671 a proximity sensor utilizing a capacitor determines the presence or absence of a material. In U.S. Pat. No. 5,556,663 a fluorophore is added to or chemically attached to a curable release coating applied to a substrate and exposed to an ultraviolet light source to monitor the cure of coated substrates such as silicone release liners. In U.S. Pat. No. 5,343,146 magnetic flux densities utilizing eddy current effects are sensed to measure coating-thickness for both nonferrous coatings on ferrous substrate and nonconductive coatings on conductive nonferrous substrate. In U.S. Pat. No. 6,034,775 optical or luminescence systems, principally polarized light, is used to screen a catalyst array located at defined regions on a substrate for use in synthesized combinatorial chemistry methods by varying the light intensity. In U.S. Pat. No. 5,185,773 an x-ray technique fluorescing lead with gadolinium (Gd-153) and sensing attenuation of the rays is used to nondestructively test the substrate of a catalytic converter to determine the amount of platinum present, including zero, on the converter substrate in a single pass. Generally, a number of the mentioned prior art sensors and systems are not of the type that can be readily implemented in or are suitable for inclusion on a vehicle as an OBD system. i.e., x-ray attenuation measurements. Many of the sensor systems are active, particularly the curing arrangements, in that a chemical reaction is forced to occur which results in a sudden physical change in state that is detected. That is the sensors disclosed are not shown or disclosed as suitable for use in a method whereat the sensor is detecting a physical aging characteristic of the catalyst correlated to a chemical active state of the catalyst or a method whereat a physical wearing away of the catalyst is detected relative to a normally aged chemical condition of the catalyst.
Accordingly it is a principle object of the invention to provide an indirect sensor system which determines if a catalyst applied to a substrate is functioning as the catalyst ages.
This object along with other features and advantages of the invention is broadly achieved in a method for determining the catalytic activity of a catalyst applied to a substrate over which a stream of fluid (liquid or gas) contacting the catalyst flows. The method includes the steps or acts of a) providing a sensor generating signals indicative of a physical characteristic of the catalyst; b) setting a threshold against which the sensor signals are compared, the threshold indicative of the chemical conversion efficiency at which the catalyst reacts with the fluid stream when the catalyst normally ages to approach a steady state conversion efficiency; c) determining from the deviation between the sensor signal and the threshold signal when the sensor signal drops below the threshold signal the quantity of catalyst present on the substrate; and d)activating a warning when the quantity of catalyst present, as determined in step (c) drops below a set value. By using one sensor signal to sequentially detect both a chemical and physical condition of the catalyst, the method is able to discern when the catalyst has aged to an unacceptable condition.
In accordance with an important object of the invention a method or system is provided for determining if a vehicular ozone depletion system is functioning to remove ozone from atmospheric air. The ozone depletion system includes a catalyst containing MnO2 applied as a coating to a heat exchange surface in the vehicle over which atmospheric air passes. The method includes the steps of:
a) sensing the presence of the MnO2 coating on the heat exchange surface and
b) activating an alarm in the vehicle when the catalyst is no longer present on the heat exchange surface.
In accordance with another important feature of the invention, the method includes the step of sensing a physical characteristic of the catalyst coating to determine i) not only its presence or absence from the heat exchange surface to determine a nonfunctioning ozone depletion system, but ii), optionally, or in addition, the relative efficiency of the ozone depletion system to convert ozone to a benign chemical or compound to determine a catastrophic failure of the ozone depletion system.
In accordance with another general feature of the invention, the sensing step includes sensing a physical characteristic of the catalyst coating selected from the group consisting of electrical conductivity, radiation absorption, radiation emission and radiation transmission whereby optical, electrical and combined optical and electrical OBD systems can be constructed to determine whether an ozone removal system based on a catalyst coating is functioning and/or measure the efficiency of the ozone removal system.
In accordance with a more specific feature of the invention, the sensing step includes the steps of providing an electrical power supply; connecting the power supply to an electrical circuit extending through a portion of the catalyst coating to cause electrons to flow through a portion of the catalyst coating when the power supply is activated; and, sensing a change or an absolute value in one or more circuit parameters selected from the group consisting of voltage, resistance or current to determine when the catalyst coating is no longer present.
In accordance with a more specific feature of the invention, a method is provided for determining when a catalyst coating containing MnO2 applied as a thin layer to the fins of a vehicular radiator ceases to remove ozone from atmospheric air passing through the radiator during the life of the radiator. The method includes the steps of providing an insulated conductor having insulation partially removed over an exposed section. The insulated conductor is embedded within the catalyst coating so that the conductor insulation is in contact with (or closely adjacent to) a radiator fin and the exposed portion of the conductor section is embedded within and contacts only the catalyst coating. An electrical power source is connected between the insulated conductor and the radiator so that an electrical circuit extends from the power source through the electrical conductor and catalyst coating to the radiator. The electrical circuit is then sensed to determine when a set change in a circuit characteristic i.e., voltage, resistance or current, occurs in which instance, a warning signal is outputted.
In accordance with another aspect of the invention, the general sensing step in the general method described above further includes the steps of providing a light source and a light detector adjacent to the front or back face of the radiator. The method further includes the steps of directing light from the light sensor against at least a portion of the radiator having the coating applied thereto when the radiator was new (or rebuilt) and sensing the incident light from the light source after it strikes the radiator by the light detector. The method then determines if the intensity of the signal outputted from the light detector is within a given range which in the first instance corresponds to the absence of the catalyst coating on the sensed portion of the radiator so that an alarm within the vehicle can be activated.
In accordance with an important aspect of the invention, the set range may also correspond to a set efficiency percentage at which the catalyst coating removes ozone and encompasses an efficiency reduction caused by a wear factor selected from the group consisting of i) a loss of catalyst coating on the radiator; ii) a poisoning of catalyst coating by contaminant deposits; and, iii) a poisoning of the catalyst coating by contaminant deposits in combination with a loss of catalyst coating.
In accordance with another aspect of the invention, the light source is an LED emitting visible or near infra-red light incident to a number of fins and the detector is an inexpensive photodiode sensing reflected light resulting in an averaged signal for a number of sensed radiator fins whereby an inexpensive OBD system results that is somewhat insensitive to a localized failure which could otherwise result in false readings.
In accordance with yet another aspect of the invention, the method includes the step of adding a marker to the catalyst coating to enhance sensed physical characteristics of the catalyst coating. Preferably, the marker includes a tag added to and uniformly dispersed within the catalytic coating when formulating the catalytic coating. In the electrical system, the marker can include various metallic particles enhancing the electrical conductivity of the circuit through the catalyst coating. In the optical system, the marker can include various phosphors and light absorbing material within specific wavelengths such as material absorbing light near the IR range to detect the presence or absence of the catalyst coating from the radiator. Still further, the tag can include heat activated radiation emission (thermochrome) substances, the detection of which insures that the catalyst coating is present on the radiator. Alternatively, the marker could include an optically reflective or electrically conductive strip applied between the heat exchanger and the catalyst coating providing signature detector signals should the catalyst coating be removed from the heat exchanger surface. The strip has specific application to installations where the heat exchanger surface is not an aluminum or brazed aluminum material which is highly electrically conductive and optically reflective.
It is a general object of the invention to determine when the efficiency of an aged catalyst applied as a coating on a substrate has dropped below an acceptable level.
It is another object of the invention to physically sense a characteristic of a catalyst coating applied to a heat exchange surface in an ozone depletion system to determine the efficiency of the system to deplete ozone from a gas passing over the catalyst coating.
It is an object of the invention to sense the presence or absence of a catalyst coating to determine if an ozone depleting system is functioning to remove ozone from a gas passing over the catalyst coating.
A specific object of the invention is to provide a system which determines the presence of a catalyst coating or the efficiency of an aged catalyst coating by monitoring response of changes in physical characteristics of the catalyst coating as a result of changes in temperature, i.e., a marker added to the coating that changes color with heat or the loss of moisture from the catalyst and its effect on electrical measurements, e.g. decrease with resistance on heating.
Yet another object of the invention is to formulate an ozone depleting catalyst with a material having physical properties that can be detected by a sensor to determine the functioning and/or efficiency of an ozone depleting system.
Another object of the invention is to provide an OBD system for vehicular application using passive sensing techniques to determine when a catalyst coating applied to a substrate has exceeded a normal, aged steady-state conversion efficiency.
Still another object of the invention is to provide a detector system for determining whether a stationary or vehicular ozone depletion system is functioning.
A more specific object of the invention is to provide an OBD system which senses an electrical characteristic of an ozone depleting catalyst coating applied to a heat exchange surface on a moving vehicle to determine if the catalyst coating is functioning to remove ozone and/or the efficiency of the catalyst coating to remove ozone from air passing over the catalyst coating.
Yet another specific object of the invention is to provide an OBD system which senses a radiation characteristic of an ozone depleting catalyst coating applied to a heat exchange surface on a moving vehicle to determine if the catalyst coating is functioning to remove ozone and/or the efficiency of the catalyst coating to remove ozone from air passing over the catalyst coating.
Still yet another object of the invention is to provide an indirect sensing OBD system which determines the functioning and/or efficiency of an ozone depletion system applied to a moving vehicle which is inexpensive and robust.
A still further object of the invention is to provide an indirect measuring OBD system monitoring the functioning of an ozone depletion system at sensitivities correlated to ozone depletion measurements in the range of 100 ppb.